The long-term objective of this research is to establish ultrasound as a safe, effective, and non-invasive method for assessing fracture risk, an important component in clinical management of osteoporosis. Osteoporosis afflicts over 20 million people in the U.S., responsible for more than 275,000 hip fractures annually. Currently, the primary means for assessment relies on densitometric techniques. These methods subject the patient to ionizing radiation, are relatively expensive, and do not always provide good estimates of bone strength. Ultrasound offers several potential advantages. It is non-ionizing and relatively inexpensive. Moreover, since ultrasound is a mechanical wave and interacts with bone in a fundamentally different manner than electromagnetic radiation, it may be able to provide more accurate estimates of bone strength compared with current densitometric methods. The goal of this research is to significantly improve the effectiveness of current ultrasonic bone assessment techniques by demonstrating the feasibility of ultrasonic arrays for obtaining precise measurements of ultrasonic parameters. The objective is to use an ultrasonic array based system to obtain highly reproducible measurements of novel ultrasonic parameters known as net time delay and mean time duration and to relate these variations to local variations in bone mineral density and trabecular architecture. The specific aims are to measure the local variations in the ultrasonic parameters using 3D computer simulations of ultrasound propagation through 3D images of human calcanei (heel bones), obtained using 3D micro-computed tomograph and quantitatively relate them to the local variations in bone mineral density and architecture as measured by fabric. [unreadable] [unreadable]